Non-aqueous electrolyte

Abstract

The present invention provides electrolytes for use in electronic devices which contain imidazolium salts in combination with high boiling aprotic solvents having lower flammability and lower toxicity than acetonitrile electrolytes.

What is claimed is: 
     
       1. An electrolyte for electronic devices comprising at least one conductive salt consisting of:
 a) a cation which is an imidazolium compound of the formula: 
 
       
         
           
           
               
               
           
         
         wherein R 1 , R 2 , R 3 , R 4  and R 5  are the same or different and are selected from the group consisting of hydrogen, an alkyl of 1-4 carbon atoms and fluoroalkyl, and 
         b) an anion selected from the group consisting of triflate, tetrafluoroborate, hexafluoroborate and fluorohydrogen fluoride, 
         c) a solvent comprising at least one member of the group consisting of ethylene carbonate, propylene carbonate, dimethyl acetamide, dimethyl formamide and gamma butyrolactone, and 
         d) a compound selected from the group consisting of methylene chloride, methylacetate and methyl formate in the amount of about 1-15 wt %, said salt being in a concentration of at least 1.5 M. 
       
     
     
       2. The electrolyte of  claim 1  wherein said salt is 1,3-dimethylimidazolium tetrafluoroborate. 
     
     
       3. The electrolyte of  claim 2  wherein the solvent is ethylene carbonate and gamma butyrolactone. 
     
     
       4. The electrolyte of  claim 3  wherein said solvent comprises 30 to 70% by weight of ethylene carbonate. 
     
     
       5. The electrolyte of  claim 3  which includes about 3% by weight of a member selected from the group consisting of methyl acetate, methylene chloride, methyl formate and acetonitrile. 
     
     
       6. The electrolyte of  claim 1  where the salt is selected from the group consisting of 1,3-dimethylimidazolium tetrafluoroborate and 1-ethyl-3-methylimidazolium tetrafluoroborate. 
     
     
       7. The electrolyte of  claim 6  wherein the salt concentration is 1.5 to 4.5 M. 
     
     
       8. The electrolyte of  claim 1  including about 3% by weight of acetonitrile. 
     
     
       9. In an electronic device containing a non-aqueous electrolyte, wherein the improvement comprises the electrolyte is the electrolyte of  claim 1 . 
     
     
       10. An electrolyte for electronic devices comprising at least one conductive salt consisting of:
 a) a cation which is an imidazolium compound of the formula: 
 
       
         
           
           
               
               
           
         
         wherein R 1 , R 2 , R 3 , R 4  and R 5  are the same or different and are selected from the group consisting of hydrogen, an alkyl of 1-4 carbon atoms and fluoroalkyl, and 
         b) an anion selected from the group consisting of triflate, tetrafluoroborate, hexafluoroborate and fluorohydrogen fluoride, 
         c) a solvent comprising at least one member of the group consisting of ethylene carbonate, propylene carbonate, dimethyl acetamide, dimethyl formamide and gamma butyrolactone, and 
         d) about 1 to 15% by weight of methyl triethylammonium tetrafluoroborate, dimethyldiethylammonium tetrafluoroborate, or trimethylethylammonium tetrafluoroborate, 
       
       said salt being in a concentration of at least 1.5 M.